1. Field of the Invention
This invention relates to an image stabilizing device for preventing the image blur of an optical instrument such as a camera resulting from hand vibration.
2. Related Background Art
In recent optical instruments such as cameras, almost all of functions necessary for photographing such as the determination of exposure and focusing are automatized and failure attributable to the photographing function has become very rare, and recently, the development of cameras in which failure in photographing attributable to any other factor than the photographing function, for example, the blur of a photographed image caused by vibration such as hand vibration, is automatically suppressed has been put forward.
Usually, to prevent vibration from occurring to a photographed image even if hand vibration occurs with the release of a camera shutter, it is necessary that means capable of detecting the vibration of the camera and properly accomplishing the correction of image blur on the basis of the detected information, i.e., an image stabilizing device, be carried on the camera.
FIG. 18 of the accompanying drawings shows in schematic block diagram an example of an image stabilizing device according to the prior art. First describing the vibration detecting means, this is constructed as optical angle deviation detecting means. That is, a case 701 enclosing therein liquid whose viscosity or the like is suitably selected and provided so as to move with a camera (or a lens barrel) has therein a mechanism supporting a float 702 freely rotatable about a rotary shaft 703, and assuming, for example, that vibration has occurred to the camera (lens barrel) and this camera has rotated by .theta..sub.in in relative to the coordinates system of absolute space, the case 701 moves with the camera. In contrast, the liquid in the case maintains its stationary state relative to the absolute space by its inertia force. Thus, the float 702 and the case 701 have rotated by .theta..sub.in in corresponding to said vibration.
So, by light from a light emitting element 706 fixedly provided on the camera (lens barrel) being reflected by the float 702 and the reflected light being received by a light receiving element 705, the angle deviation of said vibration can be detected in a position detecting circuit 704 connected to the light receiving element 705.
On the other hand, description will now be made of a mechanism for making an image on the image plane apparently stationary. In the example of the prior art shown in FIG. 18, liquid having a predetermined refractive index is enclosed in an accordion-shaped container formed by connecting two transparent plates together by bellows, thereby constituting a variable vertical angle prism 707, which is used as optic axis eccentricity means. The transparent plate on the object side is suitably tilted relative to the fixed transparent plate adjacent to a photo-taking lens 708 by an actuator 713 which is a solenoid so that the photographing optic axis can be changed. That is, by the transparent plate on the object side of the variable vertical angle prism 707 rotating by .theta..sub.out, a photographing optical path passing through the photo-taking lens 708 to the surface 709 of film rotates relative to the optic axis in proportion to said Gout and in accordance with a proportion constant determined by the refractive index of the enclosed liquid.
As described above, in the camera of FIG. 18, vibration occurring to the camera is detected by the optical angle deviation detecting means using the rotatable float 702 and the vertical angle of the variable vertical angle prism 707 is varied by an angle corresponding to the detected vibration, whereby even when the camera vibrates, the incident light from an object can always be directed to the same position on the surface 709 of the film, thereby suppressing the blur of a photographed image.
In the prior-art device of FIG. 18, the actual state of the angle deviation .theta..sub.out effected by the variable vertical angle prism 707 is detected by a position detecting circuit 712 disposed near the variable vertical angle prism 707, and an amount of output indicative of said angle deviation .theta..sub.out is subtracted from a signal indicative of the angle .theta..sub.in which is the output of the position detecting circuit 704 detected as the vibration of the camera, and said subtracted output is amplified by an amplifier circuit 714 and thereafter is input to a driver circuit 716 through a phase compensator circuit 715.
Accordingly, the driving of the actuator 713 is feedback-controlled thereby and accurate image stabilization control is realized.
Now, in the image stabilizing device described above with reference to FIG. 18, the starting or termination of the image stabilizing operation are effected, for example, by the ON/OFF of a manually operated switch extraneously operated which is designated by 720 in FIG. 18, and this forms means for actually starting or terminating the operation.
That is, the input from the angle deviation detecting means to the actuator 713 is effected by the ON/OFF of the manually operated switch 720.
In such a construction, when the switch 720 is closed when inputting the detection output from the above-described optical angle deviation detecting means to the driver 716 of the variable vertical angle prism (that is, starting the image stabilization), the signal indicative of the vibrated state which is detected by the angle deviation detecting means is intactly input to the driver 716.
However, such control, although not said to be unsuitable as a device which satisfies the image stabilizing function, has led to the problem that it results in a system inconvenient for use when viewed from the viewpoint of the use of the camera carrying such device thereon.
Considering, for example, a case where the switch 720 is closed with the position detection signal from the angle deviation detecting means being greatly off the usual central position and image stabilization control is started, the transparent plate on the object side of the variable vertical angle prism 707 is suddenly displaced from its inclined state to its parallel state.
This results in a sudden change in the optical path, and in a camera of a type such as TTL in which an object is seen through a viewfinder and a photo-taking optical system, there occurs the discontinuity (so-called skip) of the viewfinder image, and this has led to the disadvantage of giving the photographer a great feeling of physical disorder.